Waferless automatic cleaning after barrier removal

ABSTRACT

A method for forming features in dielectric layers and opening barrier layers for a plurality of wafers and cleaning an etch chamber after processing and removing each wafer of the plurality of wafers is provided. A wafer of the plurality of wafers is placed into the etch chamber wherein the wafer has a barrier layer over the wafer and a dielectric layer over the barrier layer. The dielectric layer is etched. The barrier layer is opened. The wafer is removed from the etch chamber. A waferless automatic cleaning of the etch chamber without the wafer is provided. The waferless automatic cleaning comprises providing a waferless automatic cleaning gas comprising oxygen and nitrogen to the etch chamber and forming a waferless automatic cleaning plasma from the waferless automatic cleaning gas to clean the etch chamber.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application and claims priority of U.S.patent Ser. No. 10/828,065, entitled “WAFERLESS AUTOMATIC CLEANING AFTERBARRIER REMOVAL,” filed on Apr. 19, 2004, naming Yao et al. asinventors, which is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to semiconductor devices. Relates to the cleaningof etch chambers after a wafer has been removed to improve etchperformance.

2. Description of the Related Art

In the formation of semiconductor devices, a barrier layer is etched.Such barrier layers may be silicon nitride SiN. The low power etching ofthe barrier layer may cause deposition on the etch chamber. It would bedesirable to provide a process that cleans the deposition from the etchchamber.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention, a method for forming features in dielectric layersand opening barrier layers for a plurality of wafers and cleaning anetch chamber after processing and removing each wafer of the pluralityof wafers is provided. A wafer of the plurality of wafers is placed intothe etch chamber wherein the wafer has a barrier layer over a conductivelayer over the wafer and a dielectric layer over the barrier layer. Thedielectric layer is etched. The barrier layer is opened. The wafer isremoved from the etch chamber. A waferless automatic cleaning of theetch chamber without the wafer is provided. The waferless automaticcleaning comprises providing a waferless automatic cleaning gascomprising oxygen and nitrogen to the etch chamber and forming awaferless automatic cleaning plasma from the waferless automaticcleaning gas to clean the etch chamber.

In another manifestation of the invention a method for cleaning an etchchamber after a barrier layer opening has been performed and a wafer hasbeen removed from the etch chamber to empty the etch chamber isprovided. A waferless automatic cleaning gas comprising oxygen andnitrogen is provided to the etch chamber. A waferless automatic cleaningplasma is formed from the waferless automatic cleaning gas to clean theetch chamber.

In another manifestation of the invention, an apparatus for etching afeature in a dielectric layer and opening barrier layers for a pluralityof wafers is provided. An etch chamber is provided. An upper electrodeis provided within the etch chamber. A lower electrode is providedwithin the etch chamber. An RF source is electrically connected to atleast one of the upper electrode and lower electrode. A gas source is influid connection with the etch chamber to provide gas into the etchchamber. A controller is controllably connected to the RF source and thegas source. The controller comprises computer readable code for etchingthe dielectric layer, computer readable code for opening the barrierlayer, and computer readable code for providing a waferless automaticcleaning of the etch chamber after a wafer has been removed from theetch chamber to empty the etch chamber after the opening of a barrierlayer. The computer readable media for providing waferless automaticcleaning comprises computer readable code for providing a waferlessautomatic cleaning gas comprising oxygen and nitrogen to the etchchamber and computer readable code for forming a waferless automaticcleaning plasma from the waferless automatic cleaning gas to clean theetch chamber.

These and other features of the present invention will be described inmore details below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a high level flow chart for part of a process for forming afeature in a dielectric layer that uses the invention.

FIGS. 2A-C are a schematic cross-sectional views of part of a wafer thatmay be used in the inventive process.

FIG. 3 is a schematic view of an etch chamber that may be used in apreferred embodiment of the invention.

FIGS. 4A and 4B illustrate a computer system, which is suitable forimplementing a controller.

FIG. 5 is a more detailed flow chart of a waferless automatic cleanprocess.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

To facilitate understanding, FIG. 1 is a high level flow chart for partof a process for forming a feature in a dielectric layer that uses theinvention. A wafer is placed in an etch chamber (step 104). A dielectricetch is performed on the wafer (step 108). After the dielectric etch thebarrier layer is opened (step 112). The wafer is then removed from theetch chamber (step 116). The empty etch chamber is then subjected to awaferless automatic clean using a plasma of oxygen and nitrogen.

EXAMPLE

In an example of the invention, a wafer is placed in an etch chamber(step 104). FIG. 2A is a schematic cross-sectional view of part of awafer 200 that may be used in the inventive process. The wafer 200 inthis example comprises at least one conductive contact 204 over asubstrate 208. A barrier layer 210 is placed over the conductive contact204. If the conductive contact 204 in this example is copper. In thisexample the barrier layer is silicon nitride (SiN). In otherembodiments, the barrier layer may be silicon carbide (SiC). The barrierlayer may have dopants. A dielectric etch layer 216 is placed over thebarrier layer 210. In this example, the dielectric etch layer is asilicon oxide based dielectric layer or a low-k (k<4.0) dielectricmaterial. A photoresist mask 220 is placed over the dielectric etchlayer 216. In this example, a dual damascene feature is being formedusing a via first process. In such a process, a via 218 has been etchedinto the dielectric etch layer 216. A photoresist mask for the via etchhas been removed and a photoresist mask 220 for a trench pattern hasbeen formed. In addition, in this example, a via plug 212 has beenformed in the via 218. Although the discussed layers are shown to be ontop of each other (i.e. the photoresist mask is directly on top of thedielectric etch layer), one or more layers may be placed between suchlayers, (i.e. an anti-reflective layer may be between the photoresistmask and the dielectric etch layer). This is why in the specificationand claims various layers are described as being “over” other layers.Possible intermediate layers are not shown for the sake of clarity.

FIG. 3 is a schematic view of an etch chamber 300 that may be used foropening the barrier layer. The etch chamber 300 comprises confinementrings 302, an upper electrode 304, a lower electrode 308, a gas source310, and an exhaust pump 320. The gas source 310 comprises a dielectricetch gas source 312, a barrier open gas source 316, an oxygen gas source318, and a nitrogen gas source 319. Various gases may be used formultiple processes. In such a case, the different gas sources may becombined. For example, nitrogen may be used during the barrier open. Insuch a case, only a single nitrogen source may be provided. The variousgas sources are shown to schematically illustrate the workings of theinvention. The gas source 310 may comprise additional gas sources.Within plasma processing chamber 300, the substrate 200 is positionedupon the lower electrode 308. The lower electrode 308 incorporates asuitable substrate chucking mechanism (e.g., electrostatic, mechanicalclamping, or the like) for holding the substrate 200. The reactor top328 incorporates the upper electrode 304 disposed immediately oppositethe lower electrode 308. The upper electrode 304, lower electrode 308,and confinement rings 302 define the confined plasma volume. Gas issupplied to the confined plasma volume by the gas source 310 and isexhausted from the confined plasma volume through the confinement rings302 and an exhaust port by the exhaust pump 320. An RF source 348 iselectrically connected to the lower electrode 308. The upper electrode304 is grounded. Chamber walls 352 surround the confinement rings 302,the upper electrode 304, and the lower electrode 308. The RF source 348may comprise a 27 MHz power source and a 2 MHz power source. An ExelanDFC™dielectric etcher, which is made by LAM Research Corporation™ ofFremont, Calif., was used in this example of the invention. Differentcombinations of connecting RF power to the electrode are possible inother embodiments, such as having an RF source connected to the upperelectrode 304.

FIGS. 4A and 4B illustrate a computer system 400, which is suitable forimplementing a controller 335 used in embodiments of the presentinvention. FIG. 4A shows one possible physical form of the computersystem. Of course, the computer system may have many physical formsranging from an integrated circuit, a printed circuit board, and a smallhandheld device up to a huge super computer. Computer system 400includes a monitor 402, a display 404, a housing 406, a disk drive 408,a keyboard 410, and a mouse 412. Disk 414 is a computer-readable mediumused to transfer data to and from computer system 400.

FIG. 4B is an example of a block diagram for computer system 400.Attached to system bus 420 is a wide variety of subsystems. Processor(s)422 (also referred to as central processing units or CPUs) are coupledto storage devices, including memory 424. Memory 424 includes randomaccess memory (RAM) and read-only memory (ROM). As is well known in theart, ROM acts to transfer data and instructions uni-directionally to theCPU and RAM is used typically to transfer data and instructions in abi-directional manner. Both of these types of memories may include anysuitable of the computer-readable media described below. A fixed disk426 is also coupled bi-directionally to CPU 422; it provides additionaldata storage capacity and may also include any of the computer-readablemedia described below. Fixed disk 426 may be used to store programs,data, and the like and is typically a secondary storage medium (such asa hard disk) that is slower than primary storage. It will be appreciatedthat the information retained within fixed disk 426 may, in appropriatecases, be incorporated in standard fashion as virtual memory in memory424. Removable disk 414 may take the form of any of thecomputer-readable media described below.

CPU 422 is also coupled to a variety of input/output devices, such asdisplay 404, keyboard 410, mouse 412 and speakers 430. In general, aninput/output device may be any of: video displays, track balls, mice,keyboards, microphones, touch-sensitive displays, transducer cardreaders, magnetic or paper tape readers, tablets, styluses, voice orhandwriting recognizers, biometrics readers, or other computers. CPU 422optionally may be coupled to another computer or telecommunicationsnetwork using network interface 440. With such a network interface, itis contemplated that the CPU might receive information from the network,or might output information to the network in the course of performingthe above-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon CPU 422 or may execute over anetwork such as the Internet in conjunction with a remote CPU thatshares a portion of the processing.

In addition, embodiments of the present invention further relate tocomputer storage products with a computer-readable medium that havecomputer code thereon for performing various computer-implementedoperations. The media and computer code may be those specially designedand constructed for the purposes of the present invention, or they maybe of the kind well known and available to those having skill in thecomputer software arts. Examples of computer-readable media include, butare not limited to: magnetic media such as hard disks, floppy disks, andmagnetic tape; optical media such as CD-ROMs and holographic devices;magneto-optical media such as floptical disks; and hardware devices thatare specially configured to store and execute program code, such asapplication-specific integrated circuits (ASICs), programmable logicdevices (PLDs) and ROM and RAM devices. Examples of computer codeinclude machine code, such as produced by a compiler, and filescontaining higher level code that are executed by a computer using aninterpreter. Computer readable media may also be computer codetransmitted by a computer data signal embodied in a carrier wave andrepresenting a sequence of instructions that are executable by aprocessor.

In this example, the dielectric etch layer 220 is a silicon oxide baseddielectric. A trench etch is used to etch the dielectric etch layer(step 108) to form the trench 230, as shown in FIG. 2B. The photoresistmask 220 and plug 212 may be stripped away during or after the trenchetch.

The barrier layer is then opened (step 210), as shown in FIG. 2C. Anexample of an etch recipe for opening a SiN barrier layer is as follows:

First, the lower electrode is cooled to 30° C. A stabilization step isprovided. In this stabilization step, the chamber pressure is set to 150mTorr. No power is provided by the RF source 348. A barrier openstabilization gas flow of 200 sccm N₂, 50 sccm CF₄, and 10 sccm CHF₃ isprovided for 15 seconds.

Next, a plasma strike step is provided. The chamber pressure ismaintained at 150 mTorr. 100 watts at 27 MHz and 100 watts at 2 MHz areprovided by the RF source 348. A strike gas flow of 200 sccm N₂, 50 sccmCF₄, and 10 sccm CHF₃ is provided for 5 seconds.

Next, a main etch step is provided. The chamber pressure is maintainedat 150 mTorr. 200 watts at 27 MHz and 400 watts at 2 MHz are provided bythe RF source 348. The lower electrode is cooled to 30° C. A main etchgas flow of 200 sccm N₂, 50 sccm CF₄, 10 sccm CHF₃, and 5 sccm O₂ isprovided for 18 seconds.

Finally, an over etch step is provided. The chamber pressure ismaintained at 150 mTorr. 200 watts at 27 MHz and 400 watts at 2 MHz areprovided by the RF source 348. The lower electrode is cooled to 30° C.An over etch gas flow of 200 sccm N₂, 50 sccm CF₄, and 10 sccm CHF₃ isprovided for 17 seconds.

In this example, a post etch treatment is provided after the barrieropen, according to the following recipe. First, a stabilization step isprovided. In this stabilization step, the chamber pressure is set to 200mTorr. No power is provided by the RF source 348. The lower electrode iscooled to 30° C. A post etch treatment stabilization gas flow of 800sccm H₂ and 200 sccm Ar is provided for 20 seconds.

Next, a plasma strike step is provided. The chamber pressure ismaintained at 200 mTorr. 200 watts at 27 MHz and 300 watts at 2 MHz areprovided by the RF source 348. The lower electrode is cooled to 30° C. Astrike gas flow of 800 sccm H₂ and 200 sccm Ar is provided for 5seconds.

Finally, a main post etch treatment step is provided. The chamberpressure is maintained at 200 mTorr. 1,000 watts at 27 MHz and 0 wattsat 2 MHz are provided by the RF source 348. The lower electrode iscooled to 30° C. A main post etch treatment gas flow of 800 sccm H₂ isprovided for 15 seconds. The post etch treatment may be used to cleanpolymer and other deposits from the wafer.

The wafer 200 is removed from the etch chamber 300 (step 116). Awaferless automatic clean is then performed on the empty etch chamber300 (step 120).

FIG. 5 is a more detailed flow chart of a waferless automatic cleanprocess used in this example. A waferless automatic cleaning gascomprising oxygen and nitrogen is provided into the etch chamber 300(step 504). In this example, 1,000 sccm of N₂ and 10 sccm of O₂ isprovided. The pressure in the etch chamber in this example is maintainedat 680 mTorr. A waferless automatic cleaning plasma is formed from thewaferless automatic cleaning gas mixture (step 508). In this example,500 watts at 27 MHz and 0 watts are 2 MHz are provided by the RF source348 for 20 seconds. The resulting plasma cleans the chamber (step 512).

The flow ratio of oxygen to nitrogen is preferably between 1:200 to1:50. More preferably, the flow ratio of oxygen to nitrogen is between1:99 to 2:98. In the preferred embodiment, the waferless automaticcleaning gas consists essentially of nitrogen and oxygen. In otherembodiments, other gases or diluents may be added. Preferably, the RFsource provides more than 300 watts at a high frequency between 12-50MHz and 0-50 watts at a low frequency between 0.1-10 MHz. Morepreferably, the RF source provides between about 300-1,000 watts at ahigh frequency between 12-50 MHz and 0-25 watts at a low frequencybetween 0.1-10 MHz. Most preferably, the RF source provides about 500watts at a high frequency of about 27 MHz and about 0 watts at any lowfrequency below 10 MHz. Preferably, during the waferless automaticcleaning the chamber pressure is between 250-1,000 mTorr. Morepreferably, during the waferless automatic cleaning the chamber pressureis between 400-900 mTorr.

In the preferred embodiment, the waferless automatic cleaning is doneafter each wafer is removed after a barrier open is performed. Otherembodiments may allow less frequent waferless automatic cleaning.

The etch rate and etch uniformity were measured for each wafer for anumber wafers being processed, thus having a number of waferlessautomatic cleanings using the inventive waferless automatic cleaningprocess with a waferless automatic cleaning gas of nitrogen with 1-2%oxygen. This process was compared to other waferless automatic cleaningprocesses.

The etch rate and etch uniformity were measured for the first and twohundredth wafer being processed, where oxygen only was used for thewaferless automatic cleaning. Using a waferless automatic cleaning withonly oxygen as the waferless automatic cleaning gas caused a processshift of 12% between the first and two hundredth wafers. Etch uniformitytests using only oxygen as the waferless automatic cleaning gas showsthe uniformity changes, which indicates that either the center or edgeetch rates vary during the etching of 200 wafers. In addition, it hasbeen found that waferless automatic cleaning using only oxygen resultsin a build up of polymer on the upper electrode.

A waferless automatic cleaning was also performed using only nitrogen,without any oxygen. It was found that such a waferless automaticcleaning process did not cause polymer build up on the upper electrode,but did cause polymer build up on the lower electrode.

It has also been found that when no waferless automatic cleaning isprovided the lower electrode becomes contaminated, which causes particlecontamination.

It was found that using the inventive waferless automatic cleaning thatduring the etching of 1500 wafers there was an etch process shift ofless than 7% with a non-monotonic trend. Etch uniformity using theinventive waferless automatic cleaning was stable. Therefore theinvention provides a more consistent wafer to wafer etch rate over alarge number of wafers (i.e. greater than 1,500) and improves etch rateuniformity and stability for an individual wafer. It has been found thatthe inventive waferless automatic cleaning also prevents polymer buildup on both the upper and the lower electrode.

Without being limited by theory, it is believed that low power used inthe barrier layer open step and the chemistry of SiN providecontaminants within the etch chamber that are difficult to clean. It hasbeen found that using a waferless automatic cleaning gas of only oxygenresults in a process shift and polymer build up at the top electrodearea. On the other hand, it has been found that using a waferlessautomatic cleaning gas of only nitrogen results in polymer build up onconfinement rings and the lower electrode area. The inventive waferlessautomatic cleaning process with a mixture of nitrogen and oxygen hasbeen found to prevent process shift and polymer build up at both the topand lower electrode areas.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, modifications andvarious substitute equivalents, which fall within the scope of thisinvention. It should also be noted that there are many alternative waysof implementing the methods and apparatuses of the present invention. Itis therefore intended that the following appended claims be interpretedas including all such alterations, permutations, modifications, andvarious substitute equivalents as fall within the true spirit and scopeof the present invention.

1. An apparatus for etching features in dielectric layers and openingbarrier layers for a plurality of wafers, comprising: an etch chamber;an upper electrode with the etch chamber; a lower electrode with theetch chamber; an RF source electrically connected to at least one of theupper electrode and lower electrode; a gas source in fluid connectionwith the etch chamber to provide gas into the etch chamber; and acontroller controllably connected to the RF source and the gas sourcecomprising computer readable media, comprising: computer readable codefor etching the dielectric layer; computer readable code for opening abarrier layer; and computer readable code for providing a waferlessautomatic cleaning of the etch chamber after a wafer has been removedfrom the etch chamber to empty the etch chamber after the opening of abarrier layer, comprising: computer readable code for providing awaferless automatic cleaning gas comprising oxygen and nitrogen to theetch chamber; and computer readable code for forming a waferlessautomatic cleaning plasma from the waferless automatic cleaning gas toclean the etch chamber.
 2. The apparatus, as recited in claim 1, whereinthe computer readable code for providing the waferless automaticcleaning gas provides the waferless automatic cleaning gas with anoxygen to nitrogen flow ratio between 1:99 to 2:98.
 3. The apparatus, asrecited in claim 1, wherein the computer code for providing thewaferless automatically cleaning gas provides a waferless automaticcleaning gas consisting essentially of oxygen and nitrogen.
 4. Theapparatus, as recited in claim 1, further comprising computer code forcleaning the etch chamber after processing and removing each wafer ofthe plurality of wafers.
 5. The apparatus, as recited in claim 1,wherein the barrier layer is selected from the group of SiN and SiC. 6.The apparatus, as recited in claim 1, further comprising computer codefor providing waferless automatic cleaning each time a wafer of theplurality of wafers is removed from the etch chamber to empty the etchchamber after the barrier layer opening.
 7. The apparatus, as recited inclaim 6, wherein the waferless automatic cleaning is able to clean boththe upper electrode and the lower electrode.
 8. The apparatus, asrecited in claim 1, wherein the forming the waferless automatic cleaningplasma comprises providing more than 300 watts at a frequency between12-50 MHz.
 9. The apparatus, as recited in claim 1, wherein the formingthe waferless automatic cleaning plasma comprises maintaining a chamberpressure between 500-750 mTorr.
 10. The apparatus, as recited in claim1, wherein the barrier layer is SiN.